This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A191965 #21 Aug 04 2025 02:32:05 %S A191965 0,2,6,8,12,14,18,22,26,32,36,42,48,54,60,66,72,78,84,92,100,104,112, %T A191965 118,126,134,142,152,160,170,180,184,192,204,212,220,226,234,244,254 %N A191965 A problem of Zarankiewicz: maximal number of 1's in a symmetric n X n matrix of 0's and 1's with 0's on the main diagonal and no "rectangle" with 1's at the four corners. %C A191965 In other words, the pattern %C A191965 1...1 %C A191965 ..... %C A191965 1...1 %C A191965 is forbidden. %C A191965 Such matrices are adjacency matrices of squarefree graphs (cf. A006786). The number of matrices with a(n) ones is given by A191966 and A335820 (up to permutations of rows/columns). - _Max Alekseyev_, Jan 29 2022 %D A191965 B. Bollobas, Extremal Graph Theory, pp. 309ff. %H A191965 D. Bienstock E. Gyori, <a href="https://epubs.siam.org/doi/pdf/10.1137/0404002">An extremal problem on sparse 0-1 matrices</a>. SIAM J. Discrete Math. 4 (1991), 17-27. %F A191965 a(n) = 2 * A006855(n). - _Max Alekseyev_, Jan 29 2022 %Y A191965 Cf. A006786, A006855, A077269, A191873 A191874, A191966, A300756, A335820, A352472. %K A191965 nonn,more %O A191965 1,2 %A A191965 _R. H. Hardin_ and _N. J. A. Sloane_, Jun 18 2011 %E A191965 a(11)-a(40) computed from A006855 by _Max Alekseyev_, Jan 28 2022; Apr 02 2022; Mar 14 2023